Dear all,
I think the common meaning of "land" in climate models and in
climate observations distinguishes "terrestrial" regions from
"marine" regions. Thus, we have terrestrial plants, terrestrial
water storage, terrestrial water fluxes, terrestrial glaciers
(which seems a bit redundant), etc., and all of these comprise the
"land" surface. Thus, in CF, I think "land" should include all
it's components: vegetation, lakes, puddles, snow, glacial ice,
etc. Sea ice, on the other hand, belongs to the marine
environment and should be considered "sea".
The above division fits nicely into how most models treat these
two very different regions. Usually sea ice is part of the ocean
model (or closely coupled to it, since the ocean can move sea ice
around), and the "land model" can include all the land components,
from vegetation to snow.
I therefore think we should avoid terms as "nonsea", as that would
be identical to "land".
I agree that there seems to be a consensus that we adopt a new
standard name -- land_surface_skin_temperature .
To help users understand that it is likely to be a measure of the
same thing as "surface_temperature", at least in models, I would
modify the proposed definition along the following lines:
Definition: The land surface skin temperature is the temperature
of a land point or the land portion of a region as inferred from
infrared radiation emitted directly from the surface to space,
without being absorbed by the atmosphere. Not all of the emitted
surface radiation originates at the soil. Some comes from various
terrestrial features (e.g., vegetation, rivers, lakes, ice, snow
cover). In models the radiating temperature of the surface is
usually the "surface_temperature", which then can be taken to be
equivalent to land_surface_skin_temperature or ocean_surface_skin
temperature, depending on the underlying medium.
I would also add this last sentence to the definition of
"sea_surface_skin_temperature".
Best regards,
Karl
On 7/16/13 10:00 AM, Evan Manning
wrote:
Jim,
We're only half disagreeing. When there is a lake (or ice/snow?)
on top of the land, you are talking about the radiative surface at
the bottom of the atmosphere, not the top of the dirt. If I
understand correctly, you only make a special case for designated
oceans.
So a more precise name might be "nonsea_surface_skin_temperature".
Then if we have 50/50 land & lake with T=310 and 290:
nonsea_surface_skin_temperature=300
sea_surface_skin_temperature=(fill value)
But 50/50 land & sea with T=310 and 290:
nonsea_surface_skin_temperature=310
sea_surface_skin_temperature=290
Ice on land would presumably be counted as land but sea ice could
still be counted as either land or sea with this terminology.
so if we have 4 equal portions
1/4 non-ice-covered non-sea (land/lake/vegetation/whatever)
T=290
1/4 ice-covered non-sea T=270
1/4 non ice-covered sea T=280
1/4 ice-covered sea T=260
Then either we count sea ice as sea:
nonsea_surface_skin_temperature=280 (men of 270 and 290)
sea_surface_skin_temperature=270 (mean of 260 and 280)
Or sea ice is not sea:
nonsea_surface_skin_temperature=273.3 (men of 260, 270 and 290)
sea_surface_skin_temperature=280
-- Evan
On Tue, Jul 16, 2013 at 9:36 AM, Jim
Biard <[email protected]>
wrote:
Evan,
I'm afraid I have to disagree. I'm working with the
MODIS and VIIRS Land Surface Temperature products right
now, and they are attempting to report the temperatures of
the soil/rock/plants/water/etc themselves. The sea
surface is masked off, but temperature for water such as
lakes and rivers (and puddles) is reported. The
emissivities of the various surface constituents are used
in the algorithms that generate the products. The top
surface of the land is definitely what is of interest. To
give one example, the products are used in drought
studies, where they are used to try and determine how wet
the soil is.
Grace and peace,
Jim
The rewording specifies that puddles are "land".
What about ponds?
lakes? rivers? great lakes? Oceans?
What if we have a grid square that is 50% land at
310 K and 50% ocean at 290 K?
Would it be correct to have these two variables
associated with it:
sea_surface_skin_temperature=290
land_surface_skin_temperature=310 (i.e. T of only
the non-sea portion)
or:
sea_surface_skin_temperature=290
land_surface_skin_temperature=300 (i.e. mean T of
land & sea portions)
How does that change if instead of being 50% ocean
it is 50% lakes & rivers?
Or lots and lots of puddles?
I think what we're interested in is not so much
the top surface of the
land as the
lower boundary of the atmosphere. So I like
"surface_skin_temperature", which
could then be used with a dimension for surface
categories.
-- Evan
About a month ago, I
submitted a new standard name for the
"land_surface_skin_temperature." While I think
the consensus is now that this new name seems
acceptable for inclusion in the CF database,
there were some comments and suggestions by
various people who pointed out that the proposed
definition for this quantity could use some more
clarification and other comments which pointed
out similarities to the current name
"surface_temperature." I've attempted to
address both of these concerns by adding another
line to the definition which better defines what
the "land_surface_skin" is. My hope is that
this clears up some uncertainty about this
quantity (e.g. it is not simply the bare land
surface but also includes various media above
the land surface) and also illustrates that it
is not the same thing as the
"surface_temperature" quantity (which I
understand as idealized, infinitesimally thin
interface temperature between the air and
land/sea and not the observable quantity that
the "land_surface_skin_temperature" proposes to
be).
With this is mind, here is my latest attempt at
this new name/definition:
Standard Name: land_surface_skin_temperature
Definition: The land surface skin temperature
is the aggregate temperature of the “land
surface skin,” which is the portion of the land
surface which emits infrared radiation directly
to space through the atmosphere. The “land
surface skin” is defined as an effective layer
which includes the upper boundary of the land
combined with additional layers which may cover
the upper land boundary (e.g. vegetation,
puddles, snow, ice, man-made objects).
Canonical Units: K
Sincerely,
Jonathan
On 6/20/2013 7:56 AM, Jonathan Gregory wrote:
Dear Karl
Like Roy, I don't think we should deprecate
sea_surface_skin_temperature.
Although I cannot remember the arguments - which
must be apparent in the
mailing list archive - I do recall that it was a
careful and long discussion
with Craig which led to the introduction of the
various SST names.
Therefore adding land_surface_skin_temperature
seems fine to me if there is
a need to be precise about this as an observable
quantity, which relates
to a particular layer, even though it's very
thin. The definition should note
that if this precise meaning is not intended,
the name surface_temperature
could be used, which strictly refers to the
temperature at the interface.
Best wishes
Jonathan
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